The treatment of many injuries such as sprains, contusions, or dislocations where immediate swelling is common typically involves application of cold ice compresses or other materials to slow the flow of blood to the injured site, thus reducing swelling. After the initial trauma and swelling due to the injury have subsided, however, it is often advisable to apply heat to the injured area to promote healing. Here again, a number of expedients have been used in the past for this purpose, including hot towels or heating pads.
Therapy devices comprising a sealed envelope with a material inside that can be used for application as desired of either heat or cold (that is, the material functions as a heat source or heat sink, respectively) have been used or at least known for some time. In some embodiments, the devices are for one time use; in other embodiments the devices can be reused, for example, following heating by immersion in hot water or irradiation in a microwave oven or cooling by placement in a cooler, freezer, etc. Some illustrative examples of such therapy devices are disclosed in U.S. Pat. No. 3,780,537 (Spencer), U.S. Pat. No. 3,874,504 (Verakas), U.S. Pat. No. 4,462,224 (Dunshee), U.S. Pat. No. 4,854,012 (Kelley), U.S. Pat. No. 5,697,961 (Kiamil), and U.S. Pat. No. 5,843,145 (Brink).
A number of heat source/sink materials have been suggested for use in therapy devices. Among the desired performance criteria are that the material exhibit a desirable degree of conformability throughout the useful temperature range so that it can be conformed to the injury location to provide effective therapeutic treatment. One commonly used gel that is currently frequently used in hot/cold compresses is petroleum-based propylene glycol. Though well performing, this material is derived from petroleum and thus does not come from a sustainable source. In addition, it is becoming more expensive.